Melanoma, the most serious type of skin cancer, develops in the cells (melanocytes) that produce melanin — the pigment that gives your skin its color. Melanoma can also form in your eyes and, rarely, in internal organs, such as your intestines.

The exact cause of all melanomas isn't clear, but exposure to ultraviolet (UV) radiation from sunlight or tanning lamps and beds increases your risk of developing melanoma. Limiting your exposure to UV radiation can help reduce your risk of melanoma.

The risk of melanoma seems to be increasing in people under 40, especially women. Knowing the warning signs of skin cancer can help ensure that cancerous changes are detected and treated before the cancer has spread. Melanoma can be treated successfully if it is detected early.

Melanomas can develop anywhere on your body. They most often develop in areas that have had exposure to the sun, such as your back, legs, arms and face.

Melanomas can also occur in areas that don't receive much sun exposure, such as the soles of your feet, palms of your hands and fingernail beds. These hidden melanomas are more common in people with darker skin.

The first melanoma signs and symptoms often are:

A change in an existing mole

The development of a new pigmented or unusual-looking growth on your skin

Melanoma doesn't always begin as a mole. It can also occur on otherwise normal-appearing skin.

Normal moles

Normal moles are generally a uniform color — such as tan, brown or black — with a distinct border separating the mole from your surrounding skin. They're oval or round and usually smaller than 1/4 inch (about 6 millimeters) in diameter — the size of a pencil eraser.

Most people have between 10 and 45 moles. Many of these develop by age 50, although moles may change in appearance over time — some may even disappear with age.

Unusual moles that may indicate melanoma

To help you identify characteristics of unusual moles that may indicate melanomas or other skin cancers, think of the letters ABCDE:

A is for asymmetrical shape. Look for moles with irregular shapes, such as two very different-looking halves.

B is for irregular border. Look for moles with irregular, notched or scalloped borders — characteristics of melanomas.

C is for changes in color. Look for growths that have many colors or an uneven distribution of color.

D is for diameter. Look for new growth in amole larger than 1/4 inch (about 6 millimeters).

E is for evolving. Look for changes over time, such as a mole that grows in size or that changes color or shape. Moles may also evolve to develop new signs and symptoms, such as new itchiness or bleeding.

Cancerous (malignant) moles vary greatly in appearance. Some may show all of the changes listed above, while others may have only one or two unusual characteristics.

Hidden melanomas

Melanomas can also develop in areas of your body that have little or no exposure to the sun, such as the spaces between your toes and on your palms, soles, scalp or genitals. These are sometimes referred to as hidden melanomas because they occur in places most people wouldn't think to check. When melanoma occurs in people with darker skin, it's more likely to occur in a hidden area.

Hidden melanomas include:

Melanoma under a nail. Acral-lentiginous melanoma is a rare form of melanoma that can occur under a fingernail or toenail. It can also be found on the palms of the hands or the soles of the feet. It's more common in blacks and in other people with darker skin pigment.

Melanoma in the mouth, digestive tract, urinary tract or vagina. Mucosal melanoma develops in the mucous membrane that lines the nose, mouth, esophagus, anus, urinary tract and vagina. Mucosal melanomas are especially difficult to detect because they can easily be mistaken for other far more common conditions.

Melanoma in the eye. Eye melanoma, also called ocular melanoma, most often occurs in the uvea — the layer beneath the white of the eye (sclera). An eye melanoma may cause vision changes and may be diagnosed during an eye exam.

When to see a doctor

Make an appointment with your doctor if you notice any skin changes that seem unusual.

Normally, skin cells develop in a controlled and orderly way — healthy new cells push older cells toward your skin's surface, where they die and eventually fall off. But when some cells develop DNA damage, new cells may begin to grow out of control and can eventually form a mass of cancerous cells.

Just what damages DNA in skin cells and how this leads to melanoma isn't clear. It's likely that a combination of factors, including environmental and genetic factors, causes melanoma. Still, doctors believe exposure to ultraviolet (UV) radiation from the sun and from tanning lamps and beds is the leading cause of melanoma.

UV light doesn't cause all melanomas, especially those that occur in places on your body that don't receive exposure to sunlight. This indicates that other factors may contribute to your risk of melanoma.

Factors that may increase your risk of melanoma include:

Fair skin. Having less pigment (melanin) in your skin means you have less protection from damaging UV radiation. If you have blond or red hair, light-colored eyes, and freckle or sunburn easily, you're more likely to develop melanoma than is someone with a darker complexion. But melanoma can develop in people with darker complexions, including Hispanics and blacks.

A history of sunburn. One or more severe, blistering sunburns can increase your risk of melanoma.

Excessive ultraviolet (UV) light exposure. Exposure to UV radiation, which comes from the sun and from tanning lights and beds, can increase the risk of skin cancer, including melanoma.

Living closer to the equator or at a higher elevation. People living closer to the earth's equator, where the sun's rays are more direct, experience higher amounts of UV radiation than do those living in higher latitudes. In addition, if you live at a high elevation, you're exposed to more UV radiation.

Having many moles or unusual moles. Having more than 50 ordinary moles on your body indicates an increased risk of melanoma. Also, having an unusual type of mole increases the risk of melanoma. Known medically as dysplastic nevi, these tend to be larger than normal moles and have irregular borders and a mixture of colors.

A family history of melanoma. If a close relative — such as a parent, child or sibling — has had melanoma, you have a greater chance of developing a melanoma, too.

Weakened immune system. People with weakened immune systems, such as those who've undergone organ transplants, have an increased risk of skin cancer.

Start by seeing your family doctor or a general practitioner if you notice any skin changes that concern you. Depending on your situation and the outcome of any tests, you may be referred to a doctor who specializes in skin diseases (dermatologist) or to a doctor who specializes in cancer treatment (oncologist).

Because appointments can be brief, and because there's often a lot of ground to cover, it's a good idea to be well-prepared for your appointment. Here's some information to help you get ready and know what to expect from your doctor.

What you can do

Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance, such as restrict your diet.

Write down any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.

Make a list of all medications, vitamins or supplements you're taking.

Take a family member or friend along. Sometimes it can be difficult to remember all the information provided during an appointment. Someone who accompanies you may remember something that you missed or forgot.

Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions can help you make the most of your time together. List your questions from most important to least important, in case time runs out. For melanoma, some basic questions to ask your doctor include:

Do I have melanoma?

How large is my melanoma?

How deep is my melanoma?

Has my melanoma spread beyond the area of skin where it was first discovered?

What additional tests do I need?

What are my treatment options?

Can any treatment cure my melanoma?

What are the potential side effects of each treatment option?

Is there one treatment you feel is best for me?

How long can I take to decide on a treatment option?

Should I see a specialist? What will that cost, and will my insurance cover it?

Are there any brochures or other printed material that I can take with me? What websites do you recommend?

What will determine whether I should plan for a follow-up visit?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask other questions during your appointment.

Skin cancer screening

Ask your doctor whether you should consider periodic screening for skin cancer. You and your doctor may consider screening options such as:

Skin exams by a trained professional. During a skin exam, your doctor conducts a head-to-toe inspection of your skin.

Skin exams you do at home. A self-exam may help you learn the moles, freckles and other skin marks that are normal for you so that you can notice any changes. It's best to do this standing in front of a full-length mirror while using a hand-held mirror to inspect hard-to-see areas. Be sure to check the fronts, backs and sides of your arms and legs. In addition, check your groin, scalp, fingernails, soles of your feet and spaces between your toes.

Some medical organizations recommend periodic skin exams by your doctor and on your own. Others don't recommend skin cancer screening exams because it's not clear whether screening saves lives. Instead, finding an unusual mole could lead to a biopsy, which, if the mole is found to not be cancerous, could lead to unnecessary pain, anxiety and cost. Talk to your doctor about what screening is right for you based on your risk of skin cancer.

Diagnosing melanoma

Sometimes cancer can be detected simply by looking at your skin, but the only way to accurately diagnose melanoma is with a biopsy. In this procedure, all or part of the suspicious mole or growth is removed, and a pathologist analyzes the sample.

Biopsy procedures used to diagnose melanoma include:

Punch biopsy. During a punch biopsy, your doctor uses a tool with a circular blade. The blade is pressed into the skin around a suspicious mole, and a round piece of skin is removed.

Excisional biopsy. In this procedure, the entire mole or growth is removed along with a small border of normal-appearing skin.

Incisional biopsy. With an incisional biopsy, only the most irregular part of a mole or growth is taken for laboratory analysis.

The type of skin biopsy procedure you undergo will depend on your situation. Doctors prefer to use punch biopsy or excisional biopsy to remove the entire growth whenever possible. Incisional biopsy may be used when other techniques can't easily be completed, such as if a suspicious mole is very large.

Melanoma stages

If you receive a diagnosis of melanoma, the next step is to determine the extent (stage) of the cancer. To assign a stage to your melanoma, your doctor will:

Determine the thickness. The thickness of a melanoma is determined by carefully examining the melanoma under a microscope and measuring it with a special tool (micrometer). The thickness of a melanoma helps doctors decide on a treatment plan. In general, the thicker the tumor, the more serious the disease.

See if the melanoma has spread. To determine whether your melanoma has spread to nearby lymph nodes, your surgeon may recommend a procedure known as a sentinel node biopsy.

During a sentinel node biopsy, a dye is injected in the area where your melanoma was removed. The dye flows to the nearby lymph nodes. The first lymph nodes to take up the dye are removed and tested for cancer cells. If these first lymph nodes (sentinel lymph nodes) are cancer-free, there's a good chance that the melanoma has not spread beyond the area where it was first discovered.

Cancer can still recur or spread, even if the sentinel lymph nodes are free of cancer.

Other factors may go into determining the aggressiveness of a melanoma, including whether the skin over the area has formed an open sore and how many dividing cancer cells are found when looking under a microscope.

Melanoma is staged using the Roman numerals I through IV. A stage I melanoma is small and has a very successful treatment rate. But the higher the numeral, the lower the chances of a full recovery. By stage IV, the cancer has spread beyond your skin to other organs, such as your lungs or liver.

The best treatment for you depends on the size and stage of cancer, your overall health, and your personal preferences.

Treating early-stage melanomas

Treatment for early-stage melanomas usually includes surgery to remove the melanoma. A very thin melanoma may be removed entirely during the biopsy and require no further treatment. Otherwise, your surgeon will remove the cancer as well as a border of normal skin and a layer of tissue beneath the skin. For people with early-stage melanomas, this may be the only treatment needed.

Treating melanomas that have spread beyond the skin

If melanoma has spread beyond the skin, treatment options may include:

Surgery to remove affected lymph nodes. If melanoma has spread to nearby lymph nodes, your surgeon may remove the affected nodes. Additional treatments before or after surgery also may be recommended.

Chemotherapy. Chemotherapy uses drugs to destroy cancer cells. Chemotherapy can be given intravenously, in pill form or both so that it travels throughout your body.

Chemotherapy can also be given in a vein in your arm or leg in a procedure called isolated limb perfusion. During this procedure, blood in your arm or leg isn't allowed to travel to other areas of your body for a short time so that the chemotherapy drugs travel directly to the area around the melanoma and don't affect other parts of your body.

Radiation therapy. This treatment uses high-powered energy beams, such as X-rays, to kill cancer cells. Radiation therapy may be recommended after surgery to remove the lymph nodes. It's sometimes used to help relieve symptoms of melanoma that has spread to another area of the body.

Biological therapy. Biological therapy boosts your immune system to help your body fight cancer. These treatments are made of substances produced by the body or similar substances produced in a laboratory. Side effects of these treatments are similar to those of the flu, including chills, fatigue, fever, headache and muscle aches.

Targeted therapy. Targeted therapy uses medications designed to target specific vulnerabilities in cancer cells. Side effects of targeted therapies vary, but tend to include skin problems, fever, chills and dehydration.

Vemurafenib (Zelboraf), dabrafenib (Tafinlar) and trametinib (Mekinist) are targeted therapy drugs used to treat advanced melanoma. These drugs are only effective if your cancer cells have a certain genetic mutation. Cells from your melanoma can be tested to see whether these medications may help you.

You can reduce your risk of melanoma and other types of skin cancer if you:

Avoid the sun during the middle of the day. For many people in North America, the sun's rays are strongest between about 10 a.m. and 4 p.m. Schedule outdoor activities for other times of the day, even in winter or when the sky is cloudy.

You absorb UV radiation year-round, and clouds offer little protection from damaging rays. Avoiding the sun at its strongest helps you avoid the sunburns and suntans that cause skin damage and increase your risk of developing skin cancer. Sun exposure accumulated over time also may cause skin cancer.

Wear sunscreen year-round. Sunscreens don't filter out all harmful UV radiation, especially the radiation that can lead to melanoma. But they play a major role in an overall sun protection program.

Use a broad-spectrum sunscreen with an SPF of at least 15. Apply sunscreen generously, and reapply every two hours — or more often if you're swimming or perspiring. The American Academy of Dermatology recommends using a broad-spectrum, water-resistant sunscreen with an SPF of at least 30.

Become familiar with your skin so that you'll notice changes. Examine your skin regularly for new skin growths or changes in existing moles, freckles, bumps and birthmarks.

With the help of mirrors, check your face, neck, ears and scalp. Examine your chest and trunk and the tops and undersides of your arms and hands. Examine both the fronts and backs of your legs and your feet, including the soles and the spaces between your toes. Also check your genital area and between your buttocks.

References

What you need to know about melanoma and other skin cancers. National Cancer Institute. http://www.cancer.gov/publications/patient-education/wyntk-skin-cancer. Accessed April 28, 2015.

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